RD125 RD200 TA125

RD125  RD200
The smallest of the RD series twins
Built from 1973-1981. Unlike the horizontally split cases of the RD250,350 & 400’s
the RD125 & RD200 retained the vertically spit cases of their predecessors.

The RD125
My first RD
Evolved from the AS3
Cousin to the TA125 Roadracer

Engine: 124cc  43X43mm air-cooled twin
Reed-valve two-stroke
Power rating 16hp@8000 (1978)
Compression Ratio 6.8:1
Fuel System: two 18mm Tekei carburetors
98mm Connecting Rod length
5-speed Transmission
Weight:228 lb
Maximim Speed: 79 mph

(Special Thanks to John Ritter for letting me borrow this European RD125 Cylinder)

European RD125 left and US RD125 right  

The RD200
Evolved from the CS5

Engine: 195cc (52x46mm)air-cooled twin
Reed-valve two-stroke
Power Rating: 22hp@7500 rpm
Compression Ratio 7.1:1
Fuel System: two 20mm Tekei carburetors
100mm Connecting Rod length
5-speed Transmission
Weight:256 lb
Maximim Speed: 90 mph

(Special Thanks to John Ritter for letting me borrow this European RD200 Cylinder)

The differences between the US125 and the later European cylinders are interesting.
-The cylinder it self became taller and the case deck height became shorter by the same amount, it received RD400 style head gaskets, the cylinder cooling fin area was increased, and it recieved new larger reedvalves.
-Instead of the boost port being just a groove it became a separate port in the sleeve above the intake but surprisingly they didn’t take advantage of the increased piston support and make the intake any larger. Nor did they lower the intake port floor as Yamaha had been doing with their 250 and 400 models.
-The divider between the transfers became much thicker. The ex port was raised .5mm and the transfers raised 1.25mm, and the EX duct  now took a sharper exit away from the centerline of the bike as well as the EX outlet dropping lower increasing the EX ducts downward angle.
-Unlike the 250,350 and 400’s there was no front to rear taper to the main transfer port openings.

The European RD 200 got all these same changes but surprisingly the US 200’s had aluminum cast against the cylinder liners to give some inner wall shape to the transfer tunnels and a nice flat ex port floor but lost both of these with the new cylinder casting. And the Ex port and transfer ports both dropped .5mm.

TA125
The TA125 Factory roadracer was based on AS3

  Offered for sale in 1974
Engine: 124cc  43X43mm air-cooled twin
Piston Port  two-stroke
Compression Ratio 7.5:1
Fuel System: two 22mm carburetors
98mm Connecting Rod length
Close ratio 5-speed Transmission
Hitachi CDI Ignition
Power rating 24bhp@12500